An urgent inquiry has been launched into how a jury trial of a migrant collapsed after the sheriff discovered the accused’s interpreter had no qualifications.

Sheriff James Tierney halted the trial of Krzysztof Kucharski on the second day after the freelance interpreter admitted her inexperience in open court, despite reassurances from the interpreting firm that she was suitably qualified. She herself had, at the start of the trial, confirmed that she was able to undertake the work.

The Scottish Court Service (SCS) hired criminology and psychology student Beata Kozlowska from Alpha Translating and Interpreting Services, the country's largest interpreting firm. Kozlowska was to interpret in the case against Kucharski, 24, at Aberdeen Sheriff Court last month, despite not possessing the Diploma in Public Service Interpreting (DPSI), the minimum industry benchmark qualification for linguists working in the public sector.

Kucharski, a car valet from Aberdeen, was alleged to have repeatedly struck his victim, Fryderyk Polak, on the body with a knife or similar instrument to his severe injury on October 12 last year. He has always maintained his innocence.

Kucharski's defence lawyer, Taco Nolf, himself a qualified translator in two foreign languages, formally objected to Kozlowska's handling of key evidence from two Polish witnesses.

The sheriff then investigated the interpreter's qualifications and deserted the case pro loco et tempore ("for the place and time") and discharged the 15-strong jury. Legal sources have indicated it is unlikely the trial could be re-staged.

The event highlighted how the SCS is continuing to use inexperienced foreign students - without the DPSI or any other interpreting qualifications - despite issuing guidelines in June that interpreters should hold the DPSI with the option in Scots law "or an equivalent qualification of similar standard".

The Sunday Herald revealed this year how mistakes are being made that could lead to miscarriages of justice, and that migrants without the DPSI are exploiting a lucrative trade in court interpreting.

Labour's justice spokeman, Richard Baker, said: "If cases are being lost like this due to translation errors then something is seriously wrong with our prosecution system. There is a principle that everyone is entitled to fair representation but from this evidence it appears this is not the case when some translation companies are involved."

In 2006, Nolf was representing in an assault case at Wick Sheriff Court that collapsed because of an error made by one of Alpha's unqualified freelance interpreters.

The lawyer said: "This is the third trial in which I have been involved that has been deserted because of incompetent interpreters, all of them supplied by the same agency."

In a statement, the SCS said that an interpreter with the DPSI plus Scottish law option qualification was "specifically requested in this case", and that Alpha provided a note to the court explaining why it thought the interpreter had other suitable qualifications, which was accepted.

It added: "The matter has been urgently raised with Alpha Translating, and we are awaiting the outcome of their internal inquiry."

Saif Shah, head of interpreting at Alpha, said it followed the guidelines in providing all relevant details about its interpreters. He added: "We are very disappointed about this development and will be investigating the matter internally and with our clients at the SCS."